Smog

World of Earth Science
COPYRIGHT 2003 The Gale Group, Inc.

Smog

Smog refers to an atmospheric condition of atmospheric instability, poor visibility, and large concentrations of gaseous and particulate air pollutants. The word "smog" is an amalgam of the words "smoke" and "fog." There are two types of smog: reducing smog characterized by sulfur dioxide and particulates, and photochemical smog characterized by ozone and other oxidants.

Reducing smog refers to air pollution episodes characterized by high concentrations of sulfur dioxide and smoke (or particulate aerosols). Reducing smog is also sometimes called London-type smog, because of famous incidents that occurred in that city during the 1950s.

Reducing smogs first became common when industrialization and the associated burning of coal caused severe air pollution by sulfur dioxide and soot in European cities. This air pollution problem first became intense in the nineteenth century, when it was first observed to damage human health, buildings, and vegetation.

There have been a number of incidents of substantial increases in human illness and mortality caused by reducing smog, especially among higher-risk people with chronic respiratory or heart diseases. These toxic pollution events usually occurred during prolonged episodes of calm atmospheric conditions, which prevented the dispersion of emitted gases and particulates. These circumstances resulted in the accumulation of large atmospheric concentrations of sulfur dioxide and particulates, sometimes accompanied by a natural fog , which became blackened by soot. The term smog was originally coined as a label for these coincident occurrences of atmospheric pollution by sulfur dioxide and particulates.

Coal smoke, in particular, has been recognized as a pollution problem in England and elsewhere in Europe for centuries, since at least 1500. Dirty, pollution-laden fogs occurred especially often in London, where they were called "peasoupers." The first convincing linkage of a substantial increase in human mortality and an event of air pollution was in Glasgow in 1909, when about 1,000 deaths were attributed to noxious smog during an episode of atmospheric stagnation. A North American example occurred in 1948 in Donora, Pennsylvania, an industrial town located in a valley near Pittsburgh. In that case, a persistent fog and stagnant air during a four-day period coupled with large emissions of sulfur dioxide and particulates from heavy industries to cause severe air pollution. A large increase in the rate of human mortality

was associated with this smog; 20 deaths were caused in a population of only 14,100. An additional 43% of the population was made ill in Donora, 10% severely so.

The most famous episode of reducing smog was the socalled "killer smog" that afflicted London in the early winter of 1952. In this case, an extensive atmospheric stability was accompanied by a natural, white fog. In London, these conditions transformed into a noxious "black fog" with almost zero visibility, as the concentrations of sulfur dioxide and particulates progressively built up. The most important sources of emissions of these pollutants were the use of coal for the generation of electricity , for other industrial purposes, and to heat homes because of the cold temperatures. In total, this smog caused 18 days of greater-than-usual mortality, and 3,900 deaths were attributed to the deadly episode, mostly of elderly or very young persons, and those with pre-existing respiratory or coronary diseases.

Smogs like the above were common in industrialized cities of Europe and North America , and they were mostly caused by the uncontrolled burning of coal. More recently, the implementation of clean-air policies in many countries has resulted in large improvements of air quality in cities, so that severe reducing smogs no longer occur there. Once the severe effects of reducing smogs on people, buildings, vegetation, and other resources and values became recognized, mitigative actions were developed and implemented.

However, there are still substantial problems with reducing smogs in rapidly industrializing regions of eastern Europe, the former Soviet Union, China, India, and elsewhere. In these places, the social priority is to achieve rapid economic growth, even if environmental quality is compromised. As a result, control of the emissions of pollutants is not very stringent, and reducing smogs are still a common problem.

To a large degree, oxidizing or Los Angeles-type smogs have supplanted reducing smog in importance in most industrialized countries. Oxidizing smogs are common in sunny places where there are large emissions of nitric oxide and hydrocarbons to the atmosphere, and where the atmospheric conditions are frequently stable. Oxidizing smogs form when those emitted (or primary) pollutants are transformed through photochemical reactions into secondary pollutants, the most important of which are the strong oxidant gases, ozone and peroxyacetyl nitrate. These secondary gases are the major components of oxidizing smog that are harmful to people and vegetation.

Typically, the concentrations of these various chemicals vary predictably during the day, depending on their rates of emission, the intensity of sunlight, and atmospheric stability. In the vicinity of Los Angeles, for example, ozone concentrations are largest in the early-to-mid afternoon, after which these gases are diluted by fresh air blowing inland from the Pacific Ocean. These winds blow the polluted smog further inland, where pine forests are affected on the windward slopes of nearby mountains. The light-driven photochemical reactions also cease at night. This sort of daily diurnal cycle is typical of places that experience oxidizing smog.

Humans are sensitive to ozone, which causes irritation and damage to membranes of the respiratory system and eyes, and induces asthma. People vary greatly in their sensitivity to ozone, but hypersensitive individuals can suffer considerable discomfort from exposure to oxidizing smog.

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Smog

Pollution A to Z
COPYRIGHT 2004 The Gale Group Inc.

Smog

Originally, the term smog was coined to describe the mixture of smoke and fog that lowered visibility and led to respiratory problems in industrial cities. More recently, the term has come to mean any decrease in air quality whether associated with reduced visibility or a noticeable impact on human health. Smog occurs when emissions of gases and particles from industrial or transportation sources are trapped by the local meteorology so the concentrations rise and chemical reactions occur. It is common to distinguish between two types of smog: London smog and Los Angeles smog.

London, or sulphurous, smog was noted following the introduction of coal into cities. It is most prevalent in the fall or winter when cool conditions naturally produce a thick surface fog. This fog mixes with the smoke and gases from burning coal to produce a dark, thick, acrid sulphurous atmosphere. Normally, the unpolluted fog would disperse during the day and be reformed at night. However, the presence of smoke particles makes the fog so thick that sunlight cannot penetrate it and so only a major change in meteorology can disperse it. The smog has been shown to contribute to an
increased death rate, primarily due to respiratory problems. The most notable example of this kind of smog occurred in London, from December 4 to 10, 1954, when some four thousand deaths in excess of normal averages resulted. A similar episode in Donora, Pennsylvania, in 1948 involved approximately twenty excess deaths. Most jurisdictions have instituted control measures to prevent this level of disaster from happening again. They have moved industries out of cities, demanded lower industrial emissions, and increased the heights of smokestacks so emissions are not trapped by local meteorology. These approaches have been largely successful, at least in controlling the most extreme events.

Los Angeles, or photochemical, smog first became apparent in the late 1940s in warm sunny cities that did not have significant coal-burning industries. It is a daytime phenomenon characterized by a white haze and contains oxidants, such as ozone, that cause eyes to water, breathing to become labored, and plants to be damaged. It results from the action of sunlight on the combination of hydrocarbons and nitrogen oxides (NOx), known as precursor gases. These are emitted from combustion sources to produce a range of oxidized products and oxidants. These compounds have been shown to produce respiratory and cardiac problems in individuals sensitive to pollution, and the damage inflicted on crops can cause significant decreases in yield. In most cities, the automobile is the primary contributor of smog's precursor gases. As the name would suggest, the most notable example of this type of smog occurs in Los Angeles, California, but it has also been experienced in a large number of cities where the weather is dry, sunlight is plentiful, and there are many automobiles or petroleum industries (e.g., Houston, Athens, and Mexico City.)

The control of photochemical smog is more difficult than for sulphurous smog because the compounds responsible for human and crop impacts are not directly emitted, but produced by chemistry in the atmosphere. Thus, greater knowledge on the emissions of gases, their reactions in the atmosphere, and their lifetime is needed. Most jurisdictions continue to focus their control strategies on reducing ozone concentrations, although particle concentrations are receiving increasing attention. Because smog results from the sunlight-initiated chemistry of hydrocarbons and nitrous oxides, the most common approach to smog control is to decrease the emission of these compounds at their source. Lower volatility gasolines and systems to capture gasoline vapors are used to reduce hydrocarbon emissions while tailpipe controls (catalytic converters) reduce emissions of both hydrocarbons and nitrogen oxides. The emission control systems of the twenty-first century mean that a car typically emits 70 percent less nitrogen oxides and 80 to 90 percent less hydrocarbons than the uncontrolled cars of the 1960s. The expected improvement in air quality, as a result of increasing controls, is estimated by using computer models of the atmosphere and its chemistry.

see also
Air Pollution;
Asthma;
Donora, Pennsylvania;
Health, Human;
Ozone.

Bibliography

Brimblecombe, Peter. (1987). The Big Smoke: A History of Air Pollution in London sinceMedieval Times. London: Methuen.

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Smog (Air Pollution)

Encyclopedia of Public Health
COPYRIGHT 2002 The Gale Group Inc.

SMOG (AIR POLLUTION)

"Smog" is a popular term used to describe polluted air. It was originally used as an abbreviation of the combination of coal smoke and fog that, along with sulfur dioxide vapor, characterized polluted air in London and other British cities in the 1950s. The term came into more widespread use as a summary description for the quite different pollution mixture of ozone (O3) and other photochemical oxidants (e.g., hydrogen peroxide, hydroxgl radical peroxy acetylnitrate) that characterized the air pollution in Southern California beginning in the 1950s, and in many other urban areas in the United States in the decades that followed. In the United Kingdom, the smog was black and acidic, while the smog in California was lighter in color and more highly oxidizing.

The black smoke in Britain was heavier in the winter months, and was most closely associated with its reducing power as a chemical (i.e., antioxidant), and with excess mortality, from chronic bronchitis and respiratory symptoms. By contrast, the California mixture was worse in the summer, and was characterized in terms of its oxidizing power. It attacked rubber and chemical polymers, and was associated with eye irritation, reduced lung function, and impaired athletic performance. In both mixtures there were fine particles that caused light to scatter and reduced the range of visibility.

In the United States, United Kingdom, and other economically developed countries in the twentieth century, the black smoke components of past pollution have largely been controlled, and the residual pollution problem is most closely related to the concentrations of light-scattering fine particles and ozone that form in the atmosphere from gaseous precursors (ie, pollutant chemicals whose reaction products have low vapor pressures and condense into fine particles). Such pollution mixtures are generally referred to as smog. While generally present at lower concentrations than in the past, these mixtures are still associated with excess cardiopulmonary mortality, morbidity, and physiologic function deficits. Attribution of the effects to specific components of the pollution mixture remains controversial, and further chemical characterization and health-effects research is now underway to resolve the remaining uncertainties.

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smog

The Columbia Encyclopedia, 6th ed.

Copyright The Columbia University Press

smog (smŏg) [smoke+fog], dense, visible air pollution. Smog is commonly of two types. The gray smog of older industrial cities like London and New York derives from the massive combustion of coal and fuel oil in or near the city, releasing tons of ashes, soot, and sulfur compounds into the air. The brown smog characteristic of Los Angeles and Denver in the late 20th cent. is caused by automobiles. Nitric oxide from automobile exhaust combines with oxygen in the air to form the brown gas nitrogen dioxide. Also, when hydrocarbons and nitrous oxides from auto emissions are exposed to sunlight, a photochemical reaction takes place that results in the formation of ozone and other irritating compounds. In some instances, atmospheric pollutants accumulate and become concentrated when air movement is stopped by a temperature inversion: Usually the air is warmer at the earth's surface and colder above; in a temperature inversion a layer of warm air forms above and holds down a layer of cool air at the ground. Smog usually results in reduced visibility, irritation of the eyes and respiratory system, and damage to paint, metal, rubber, and other materials. Prolonged smogs (generally caused by temperature inversions) are often lethal to persons with respiratory ailments. As the result of an unremitting smog in 1948 in Donora, Pa., more than 5,000 persons were reported ill and the deaths of 20 persons were recorded. In London, smog accounted for the deaths of more than 4,000 persons in 1952 and 106 persons in 1962.

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Smog

Smog

With a rotating lineup of backing musicians, though most of his early releases were one-man efforts, Bill Callahan has released work since the late 1980s under the Smog name. A pioneer of the lo-fi movement, the eclectic songwriter and minimalist musician combined elements of rock, blues, country, and experimental sounds that usually revealed a dark and hopeless view of the world. His words are largely intimate self-revelations: melancholy, often bitter pessimisms that veer between painful candor and self-parody. His low-end production style has said to have been an influence on such bands as Pavement and Guided by Voices. Throughout the 1990s, and especially since the issue of The Doctor Came at Dawn in 1996, Callahan amassed a loyal cult following, primarily in the United States and Great Britain. One of his most vocal supporters includes Lou Barlow, the indie rock guru and leader of Sebadoh and Folk Implosion.

Despite comparisons to diverse styles and other musicians, such as Neil Young and the Replacements, Callahan always hesitated to align himself with one particular genre. “It’s hard to wake up in the morning and say, ‘I’m a country musician today,’” Callahan explained to Corey duBrowa in Magnet magazine. “Or, ‘I’ll be a rock musician now’—(those) jackets don’t really fit. You can’t look at yourself in the mirror and say those things. If there’s a rock element in a song, if anything, I’ll put an opposite element in there just to balance it.” And when asked about how he feels about the music press placing him in the lo-fi category, Callahan replied, “It never meant anything to me, and I never really understood it,” as quoted by Marlene Goldman from a February, 1999, interview with the RollingStone.com website. “I don’t believe in these sorts of movements in music. I don’t even think they exist…. it’s just music, and has been since music started.”

Callahan was born in Maryland in 1966. Shortly after his birth, his family moved to England, where he lived until the age of three. The family then returned to the United States, remaining in America for the next four years. At the age of seven, Callahan returned to Knaresborough in North Yorkshire, England, for another five years, before going back to the United States at age 12. Despite his frequent moves between the two countries during his early childhood, Callahan, as an adult, regarded himself as 100 percent American. Nevertheless, the songwriter admitted that he has always felt he never really fit in anywhere he lived. During his adult life, Callahan called several cities home, including Prosperity, South Carolina, San Francisco and Sacramento, California, and Chicago, where he has lived since around 1999.

Callahan, who realized in his early twenties that he would never enjoy working in an office and wanted to maintain his freedom, began his recording career releasing a series of self-made cassette tapes on his own Disaster label under the name Smog. The first of these tapes, Macramé Gunplay, arrived in 1988, while his second cassette, Cow, was released in 1989. 1990 saw the release of three more tapes: the enigmatic, minimalist A Table Setting, Tired Tape Machine, and the primitive yet promising Sewn to the Sky. Sewn to the Sky caught the attention of Chicago’s Drag City label, echoed the Residents and Captain Beefheart. And as the vague, atmospheric title and the name Smog suggest, Callahan’s repetitive guitar riffs, complemented by his occasional and deeply subdued vocals, formed the bleak sound-scapes of notable tracks such as “Garb” and “Fruit Bats.”

After signing with Drag City, Callahan released his first EP, Floating, in 1991. Smog’s debut full-length album for Drag City, Forgotten Foundation, arrived in 1992. Though still purposefully crude in terms of musical development and production, Forgotten Foundation nonetheless showed Callahan’s song-oriented side for some tracks with more traditional arrangements, additional vocals, and more fully developed melodies, paving the way for Smog’s follow-up, Julius Caesar. Released in 1991 and recorded with musicians Cynthia Dall and Jim O’Rourke, the spare, folk-inspired Julius Caesar was Smog’s first release to earn critical acclaim. Here, Callahan incorporated cello, violin, acoustic guitar, and banjo into the mix

Released series of self-made cassettes on own Disaster label, beginning with Macramé Gunplay in 1988; signed with Chicago’s Drag City label, released EP Floating, 1991; released debut album for Drag City, Forgotten Foundation, 1992; released acclaimed album Julius Caesar, 1993; released The Couple Came at Dawn, 1996; released the more optimistic Knock Knock, 1999.

and established himself as a focused songwriter. He composed tracks that revealed both elation, as in “When You Walk,” and more commonly depression, as in “Your Wedding.” Highlights from the album included the upbeat “I Am Star Wars!,” the instrumental cello piece “One Less Star,” and the immortal “37 Push Ups.”

Smog released the six-song EP Burning Kingdom, which found Callahan further breaking with his lo-fi tendencies, in 1994. For the song “My Shell,” for example, Callahan’s words of alienation are complemented by electric guitar, cello, and drums. Other notable tracks included “My Family,” a low-key, relentless psychodrama, and “The Desert,” which tells the story of crawling through the desert without water to the accompaniment of a funeral-like organ. In 1995, Smog released another more fully-produced album entitled Wild Love, which found Callahan for the most part abandoning hopefulness—excluding the brilliant “Prince Alone in the Studio,” a metaphor for an artist’s lonely existence—in favor of a relentless, often bitter pessimism that some critics found hard to take seriously. Throughout the album, Callahan tells stories of an unhappy childhood, failed romances, and life’s disappointments in general.

In 1996, Smog released the Kicking a Couple Around EP, which opened with a solo acoustic performance of the song “Your New Friend” from a British Broadcasting Company (BBC) broadcast and also included three tracks recorded and produced in Chicago with Steve Albini. Overall, Callahan again focused on introspection, gloom, and feelings of displacement, such as in “The Orange Glow of a Stranger’s Living Room” and “I Break Horses,” a song “which can reduce strong men and women… to heaps of quivering gelatin,” according to Ben Thompson of Independent on Sunday. That same year, Callahan followed with the groundbreaking album The Doctor Came at Dawn, comprised of quiet, acoustic songs of reflection. However, Callahan admitted that unanticipated events led him to concentrate on his acoustic side for his 1996 records. “I’m really haphazard how I work. I like to work around difficulties and not really plan things,” he said to Goldman. “Like, I had a keyboard that got stolen [on tour in Barcelona]—the keyboard I used on the Wild Love album. The I made Kicking a Couple Around, which is just with acoustic guitar. It was my reaction to having my keyboard stolen.”

Callahan returned in 1997 with another mostly acoustic effort, Red Apple Falls, a country-informed album with unexpected dashes of French horns and steel guitar that bore similarities to the songs of Neil Young. Red Apple Falls took just five days to record, but included songs that reveal concepts that could take years to understand, exemplified in the tracks “Inspirational” and “I Was a Stranger.” His subsequent release, Knock Knock, appeared in 1999 and was co-produced by O’Rourke. Considered Smog’s most diverse release, Knock Knock featured orchestral qualities and members of the Chicago Children’s Choir for the chorus in tracks like “No Dancing,” as well as acoustic numbers like “Left Only With Love.” Unlike his prior work, which overwhelmingly centered around a doomed and pessimistic view of life, Knock Knock provided a more optimistic view of the world. “It’s more forward-thinking. I guess I had some realizations about not letting things crush you,” Callahan explained to duBrowa. “The fact that you can always move… you don’t have to stay in a bad place.”

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Smog

Environmental Encyclopedia
COPYRIGHT 2003 The Gale Group Inc.

Smog

A term chosen by the Glasgow public health official Des Voeux at the beginning of the twentieth century to describe the smoky fogs that characterized coal-burning cities of the time. The word is formed by adding the words smoke and fog together and has persisted as a description of this type of urban atmosphere . It has more and more been used to describe photochemical smog , the haze that became a characteristic of the Los Angeles Basin from the 1940s. "Smog" is sometimes even used to describe air pollution in general, even where there is no reduction in visibility at all. However, the term is most properly used to describe the two distinctive types of pollution that dominated the atmospheres of late nineteenth century London, England, known as winter smog, and twentieth century Los Angeles, called summer smog.

The city of London burned almost 20 million tons of coal annually by the end of the nineteenth century. Although industrialized, much coal was burned in domestic hearths, and the smoke and sulfur dioxide produced barely rose from the chimneys above the housetops. Only a few rather inaccurate measurements of the pollutant concentrations in the air were made in the last century, although they hint at concentrations much higher than what we might expect in London today.

The smogs of nineteenth-century London took the form of dense, vividly colored fogs. The smog was frequently so dense that people became lost and had to be lead home by linksmen. It is said that visibility became so restricted that fingers on an outstretched arm were invisible. The fog that rolled over window sills and into rooms became such an integral part of what we know as Victorian London that almost any Sherlock Holmes story mentions it.

With London's high humidity and incipient fog, smoke particles from coal-burning formed a nucleus for the condensation of vapor into large fog droplets. This water also serves as a site for chemical reactions, in particular the formation of sulfuric acid . Sulfur dioxide dissolved in fog droplets, perhaps aided by the presence of alkaline material such as ammonia or coal ash. Once in solution the sulfur was oxidized, a process often catalyzed by the presence of dissolved metallic ions such as iron and manganese. Dissolution
and oxidation of sulfur dioxide gave rise to sulfuric acid droplets, and it was sulfuric acid that made the smog so damaging to the health of Londoners.

London's severe smogs occurred throughout the last decades of the nineteenth century. Detective writer Robert Barr even published The Doom of London at the turn of the century, which saw the entire population of London eliminated by an apocalyptic fog. Many residents of Victorian London recognized that the fogs increased death rates, but the most infamous incident occurred in 1952, when a slow-moving anti-cyclone stalled the air over the city. On the first morning the fog was thicker than many people could ever remember. By the afternoon people noticed the choking smell in the air and started experiencing discomfort. Those who walked about in the fog found their skin and clothing filthy after just a short time. At night the treatment of respiratory cases was running at twice its normal level. The situation continued for four days.

It was difficult to describe exactly what had happened, because primitive air pollution monitoring equipment could not cope with high and rapidly changing concentrations of pollutants, but it has been argued that for short periods the smoke and sulfur dioxide concentrations may have approached ten thousand micrograms per 1.3 yd3 (1 m3). Today, in a relatively healthy city, the desired maximum is about a hundred micrograms per 1.3 yd3 in short-term exposures.

Normal death rates were exceeded by many thousands through the four-day period of the fog. Public feelings ran high, and the United Kingdom government, barraged with questions, set up an investigative committee. The Beaver Committee report eventually served as the basis for the UK Clean Air Act of 1956. This law was gradually adopted through many towns and cities of the UK and has been seen by many as a model piece of legislation. Although it is true that the classic London smog has gone, it is far from clear the extent to which this change came about through legislation rather than through broader social developments, such as the use of electricity in homes (although the act did encourage this).

Photochemical smog is sometimes called summer smog, because unlike the classical London type smog, it is more typical in summer at many localities, often because it requires long hours of sunshine to build up. When photochemical smogs were first noticed in Los Angeles, people believed them to be much the same as the smogs of London and Pittsburgh. Early attempts at control looked largely at local industry emissions. The automobile was eliminated as a likely cause because of low concentrations of sulfur in the fuel and the fact that only minute amounts of smoke were generated.

It was some time before the biochemist Arie Jan Haagen-Smit recognized that damage to crops in the Los Angeles area arose not from familiar pollutants, but from a reaction that took place in the presence of petroleum vapors and sunlight. His observations focused unwelcome attention on the automobile as an important factor in the generation of summer smog.

The Los Angeles area proved an almost perfect place for generating smogs of this type. It had a large number of cars, long hours of sunshine, gentle sea breezes to back the pollutants up against the mountains, and high level inversions preventing the pollutants from dispersing vertically.

Studies through the 1950s revealed that the smog was generated through a photolytic cycle. Sunlight split nitrogen dioxide into nitric oxide and atomic oxygen that could subsequently react and form ozone . This was the key pollutant that clearly distinguished the Los Angeles smogs from those found in London. Although the highly reactive ozone reacts rapidly with nitric oxide, converting it back into nitrogen dioxide, organic radicals produced from petroleum vapor react with nitric oxide very quickly. The nitrogen dioxide is again split by the sunlight, leading to the formation of more ozone. The cycle continues to build ozone concentrations to higher levels throughout the day.

The nitrogen oxide-ozone cycle is just one of many processes initiated in a smog of this kind. The photochemically active atmosphere contains a great number of reactive molecular fragments that lead to a range of complex organic compounds. Some of the hydrocarbon molecules of petroleum vapor are oxidized to aldehydes or ketones , such as acrolein or formaldehyde, which are irritants and suspected carcinogens. Some oxygenated fragments of organic molecules react with the nitrogen oxides present in the atmosphere. The best-known product of these reactions is peroxyacetyl nitrate , often called PAN, one of a class of nitrated compounds causing eye irritation experienced in summer smogs.

The reactions that were recognized in the Los Angeles smog are now known to occur over wide areas of the industrialized world. The production of smog of this kind is not limited to urban or suburban areas, but may occur for many hundreds of miles to the lee of cities using large quantities of liquid fuel. The importance of hydrocarbons in sustaining the processes that generate photochemical smog has given rise to control policies that recognize the need to lower the emission of hydrocarbons into the atmosphere, and hence the emphasis of the use of catalytic converters and low volatility fuels as part of air pollution control strategies.

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Smog

Smog

Smog refers to an atmospheric condition of atmospheric instability, poor visibility, and large concentrations of gaseous and particulate air pollutants. The word “smog” is an amalgam of the words “smoke” and “fog.” There are two types of smog: reducing smog characterized by sulfur dioxide and particulates, and photochemical smog characterized by ozone and other oxidants.

Reducing smog refers to air pollution episodes characterized by high concentrations of sulfur dioxide and smoke (or particulate aerosols). Reducing smog is also sometimes called London-type smog, because of famous incidents that occurred in that city during the 1950s.

Reducing smogs first became common when industrialization and the associated burning of coal caused severe air pollution by sulfur dioxide and soot in European cities. This air pollution problem first became intense in the nineteenth century, when it was first observed to damage human health, buildings, and vegetation.

There have been a number of incidents of substantial increases in human illness and mortality caused by reducing smog, especially among higher-risk people with chronic respiratory or heart diseases. These toxic pollution events usually occurred during prolonged episodes of calm atmospheric conditions, which prevented the dispersion of emitted gases and particulates. These circumstances resulted in the accumulation of large atmospheric concentrations of sulfur dioxide and particulates, sometimes accompanied by a natural fog, which be came blackenedby soot. The term smog was originally coined as a label for these coincident occurrences of atmospheric pollution by sulfur dioxide and particulates.

Coal smoke, in particular, has been recognized as a pollution problem in England and elsewhere in Europe for centuries, since at least since 1500. Dirty, pollutionladen fogs occurred especially often in London, where they were called “pea-soupers.” The first convincing linkage of a substantial increase in human mortality and an event of air pollution was in Glasgow in 1909, when about 1,000 deaths were attributed to a noxious smog during an episode of atmospheric stagnation. A North American example occurred in 1948 in Donora, Pennsylvania, an industrial town located in a valley near Pittsburgh. In that case, a persistent fog and stagnant air during a four-day period coupled with large emissions of sulfur dioxide and particulates from heavy industries caused severe air pollution. A large increase in the rate of human mortality was associated with this smog; 20 deaths were caused in a population of only 14,100. An additional 43% of the population was made ill in Donora, 10% severely so.

The most famous episode of reducing smog was the so-called “killer smog” that afflicted London in the early winter of 1952. In this case, an extensive atmospheric stability was accompanied by a natural, white fog. In London, these conditions transformed into a noxious “black fog” with almost zero visibility, as the concentrations of sulfur dioxide and particulates progressively built up. The most important sources of emissions of these pollutants were the use of coal for the generation of electricity, for other industrial purposes, and to heat homes because of the cold temperatures. In total, this smog caused 18 days of greater-than-usual mortality, and 3,900 deaths were attributed to the deadly episode, mostly of elderly or very young persons, and those with pre-existing respiratory or coronary diseases.

Smogs like the above were common in industrialized cities of Europe and North America, and they were mostly caused by the uncontrolled burning of coal. More recently, the implementation of clean-air policies in many countries has resulted in large improvements of air quality in cities, so that severe reducing smogs no longer occur there. Once the severe effects of reducing smogs on people, buildings, vegetation, and other resources and values became recognized, mitigative actions were developed and implemented.

However, there are still substantial problems with reducing smogs in rapidly industrializing regions of eastern Europe, the former Soviet Union, China, India, and elsewhere. In these places, the social priority is to achieve rapid economic growth, even if environmental quality is compromised. As a result, control of the emissions of pollutants is not very stringent, and reducing smogs are still a common problem.

To a large degree, oxidizing or Los Angeles-type smogs have supplanted reducing smog in importance in most industrialized countries. Oxidizing smogs are common in sunny places where there are large emissions to the atmosphere of nitric oxide and hydrocarbons, and where the atmospheric conditions are frequently stable. Oxidizing smogs form when those emitted (or primary) pollutants are transformed through photochemical reactions into secondary pollutants, the most important of which are the strong oxidant gases, ozone and peroxyacetyl nitrate. These secondary gases are the major components of oxidizing smog that are harmful to people and vegetation.

Typically, the concentrations of these various chemicals vary predictably during the day, depending on their rates of emission, the intensity of sunlight, and atmospheric stability. In the vicinity of Los Angeles, for example, ozone concentrations are largest in the early-to-mid afternoon, after which these gases are diluted by fresh air blowing inland from the Pacific Ocean. These winds blow the polluted smog further inland, where pine forests are affected on the windward slopes of nearby mountains. The photochemical reactions also cease at night, because sunlight is not available then. This sort of daily cycle is typical of places that experience oxidizing smog.

Humans are sensitive to ozone, which causes irritation and damage to membranes of the respiratory system and eyes, and induces asthma. People vary greatly in their sensitivity to ozone, but hypersensitive individuals can suffer considerable discomfort from exposure to oxidizing smog. However, in contrast to some of the events of reducing smog, ozone and oxidizing smog more generally do not appear to cause the death of many large people. Ozone is also by far the most important gaseous pollutant in North America, in terms of causing damage to agricultural and wild plants.

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Smog

Environmental Science: In Context
COPYRIGHT 2009 Gale

Smog

Introduction

Smog is a particularly potent type of air pollution. It is usually highly visible as a brownish or yellowish haze in the air, and although smog is often associated with large cities, it occurs around the world. Smog occurs when emissions from factories and cars mix with air under certain atmospheric conditions that trap pollutants near to the ground. Heavy traffic, warm weather, and still air tend to contribute to smog build up in cities such as Los Angeles, California. Ground level ozone is often a component of smog, and it is created by a complex series of chemical reactions catalyzed by sunlight.

Smog has a number of damaging impacts on health. The most obvious effects in a thick urban smog would be watering eyes and coughing. More serious impacts include triggering of asthma and heart attacks. Smog also reduces visibility, which can be dangerous when driving. Environmental legislation promoting cleaner air has dramatically reduced the incidence of smog in many countries, but it continues as a worldwide issue.

Historical Background and Scientific Foundations

In 1952, around 4,000 people in London, England, died as a result of the notorious Great Smog. Emissions from factories combined with smoke from people’s chimneys to create a great cloud of pollution that enveloped the city. The term smog, which means fog intensified by smoke, was coined in 1905, although the problem of the so-called “pea-souper” fogs occurring in urban areas dates back much further, and is mentioned in the work of nineteenth-century British writer Charles Dickens (1812–1870).

Smog is visible as a brownish haze polluting the air, particularly in cities and especially in the summer. It comprises an aerosol of noxious droplets and particles. One major component of smog is ozone, which is formed when nitrogen oxides and unburned hydrocarbons from motor vehicles react in the presence of sunlight to create a photochemical smog. Ozone in the stratosphere is helpful, as it absorbs ultraviolet (UV) light from the sun. Ground level ozone is a powerful pollutant that affects the eyes and lungs.

Los Angeles is a classic example of a city where climate and geographical factors create conditions for the formation of photochemical smog. The city is surrounded by mountains on three sides and has a dry, sunny climate. At night, the sky is usually clear and the ground cools fast. Air near the surface is cool, while upper layers are relatively warm. Lack of mixing of the layers forms an inversion and traps pollution from traffic close to the ground. Morning sunshine triggers a number of photochemical reactions, creating ozone. This photochemical smog is sometimes clearly visible as a brown haze by the afternoon.

Another example of smog is the Asian Brown Cloud, which is produced by burning of agricultural wastes and increases in the use of fossil fuels. The cloud covers the entire Indian sub-continent for much of the year and drifts out over the Indian Ocean at the end of the monsoon season.

Impacts and Issues

The World Health Organization (WHO) says that air pollution, including smog, claims five to six million lives per year. Fine particles in smog are linked with heart attacks, worsening asthma, lung cancer, and immune suppression. Ozone and formaldehyde cause eye irritation, coughing, chest pain, and attacks of asthma and bronchitis. Meanwhile, smog reduces visibility. If all sources of air pollution were removed from the atmos-

WORDS TO KNOW

AEROSOL: Liquid droplets or minute particles suspended in air.

INVERSION: A type of chromosomal defect in which a broken segment of a chromosome attaches to the same chromosome, but in reverse position.

OZONE: An almost colorless, gaseous form of oxygen, with an odor similar to weak chlorine, that is produced when an electric spark or ultraviolet light is passed through air or oxygen.

PHOTOCHEMICAL SMOG: A type of smog created by the action of sunlight on pollutants.

phere, people in cities could see an estimated ten times farther than they can today.

There are various legislative measures in place in the United States and elsewhere designed to reduce smog and air pollution. The 1990 Clean Air Act covers ozone, nitrogen oxides, and particles in smog. States must meet the criteria that the Environmental Protection Agency (EPA) lays down for these pollutants or take measures to clean up. Generally, this involves applying new, cleaner technology to vehicles and tackling traffic congestion. Some states such as California have gone one step farther by enacting tougher vehicle emission standards than are required by federal law.

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

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Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.

In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

Smog

The Gale Encyclopedia of Science
COPYRIGHT 2008 The Gale Group, Inc.

Smog

Smog refers to an atmospheric condition of atmospheric instability, poor visibility, and large concentrations of gaseous and particulate air pollutants. The word "smog" is an amalgam of the words "smoke" and "fog." There are two types of smog: reducing smog characterized by sulfur dioxide and particulates, and photochemical smog characterized by ozone and other oxidants.

Reducing smog

Reducing smog refers to air pollution episodes characterized by high concentrations of sulfur dioxide and smoke (or particulate aerosols ). Reducing smog is also sometimes called London-type smog, because of famous incidents that occurred in that city during the 1950s.

Reducing smogs first became common when industrialization and the associated burning of coal caused severe air pollution by sulfur dioxide and soot in European cities. This air pollution problem first became intense in the nineteenth century, when it was first observed to damage human health, buildings, and vegetation.

There have been a number of incidents of substantial increases in human illness and mortality caused by reducing smog, especially among higher-risk people with chronic respiratory or heart diseases . These toxic pollution events usually occurred during prolonged episodes of calm atmospheric conditions, which prevented the dispersion of emitted gases and particulates. These circumstances resulted in the accumulation of large atmospheric concentrations of sulfur dioxide and particulates, sometimes accompanied by a natural fog , which became blackened by soot. The term smog was originally coined as a label for these coincident occurrences of atmospheric pollution by sulfur dioxide and particulates.

Coal smoke, in particular, has been recognized as a pollution problem in England and elsewhere in Europe for centuries, since at least 1500. Dirty, pollution-laden fogs occurred especially often in London, where they were called "pea-soupers." The first convincing linkage of a substantial increase in human mortality and an event of air pollution was in Glasgow in 1909, when about 1,000 deaths were attributed to a noxious smog during an episode of atmospheric stagnation. A North American example occurred in 1948 in Donora, Pennsylvania, an industrial town located in a valley near Pittsburgh. In that case, a persistent fog and stagnant air during a four-day period coupled with large emissions of sulfur dioxide and particulates from heavy industries to cause severe air pollution. A large increase in the rate of human mortality was associated with this smog; 20 deaths were caused in a population of only 14,100. An additional 43% of the population was made ill in Donora, 10% severely so.

The most famous episode of reducing smog was the so-called "killer smog" that afflicted London in the early winter of 1952. In this case, an extensive atmospheric stability was accompanied by a natural, white fog. In London, these conditions transformed into a noxious "black fog" with almost zero visibility, as the concentrations of sulfur dioxide and particulates progressively built up. The most important sources of emissions of these pollutants were the use of coal for the generation of electricity , for other industrial purposes, and to heat homes because of the cold temperatures. In total, this smog caused 18 days of greater-than-usual mortality, and 3,900 deaths were attributed to the deadly episode, mostly of elderly or very young persons, and those with preexisting respiratory or coronary diseases.

Smogs like the above were common in industrialized cities of Europe and North America , and they were mostly caused by the uncontrolled burning of coal. More recently, the implementation of clean-air policies in many countries has resulted in large improvements of air quality in cities, so that severe reducing smogs no longer occur there. Once the severe effects of reducing smogs on people, buildings, vegetation, and other resources and values became recognized, mitigative actions were developed and implemented.

However, there are still substantial problems with reducing smogs in rapidly industrializing regions of eastern Europe, the former Soviet Union, China, India, and elsewhere. In these places, the social priority is to achieve rapid economic growth, even if environmental quality is compromised. As a result, control of the emissions of pollutants is not very stringent, and reducing smogs are still a common problem.

Oxidizing smog

To a large degree, oxidizing or Los Angeles-type smogs have supplanted reducing smog in importance in most industrialized countries. Oxidizing smogs are common in sunny places where there are large emissions to the atmosphere of nitric oxide and hydrocarbons, and where the atmospheric conditions are frequently stable. Oxidizing smogs form when those emitted (or primary) pollutants are transformed through photochemical reactions into secondary pollutants , the most important of which are the strong oxidant gases, ozone and peroxyacetyl nitrate. These secondary gases are the major components of oxidizing smog that are harmful to people and vegetation.

Typically, the concentrations of these various chemicals vary predictably during the day, depending on their rates of emission , the intensity of sunlight, and atmospheric stability. In the vicinity of Los Angeles, for example, ozone concentrations are largest in the early-tomid afternoon, after which these gases are diluted by fresh air blowing inland from the Pacific Ocean. These winds blow the polluted smog further inland, where pine forests are affected on the windward slopes of nearby mountains . The photochemical reactions also cease at night, because sunlight is not available then. This sort of daily cycle is typical of places that experience oxidizing smog.

Humans are sensitive to ozone, which causes irritation and damage to membranes of the respiratory system and eyes, and induces asthma . People vary greatly in their sensitivity to ozone, but hypersensitive individuals can suffer considerable discomfort from exposure to oxidizing smog. However, in contrast to some of the events of reducing smog, ozone and oxidizing smog more generally do not appear to cause the death of many large people. Ozone is also by far the most important gaseous pollutant in North America, in terms of causing damage to agricultural and wild plants.

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

The Chicago Manual of Style

American Psychological Association

Notes:

Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.

In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.